To achieve energy efficiency, a common goal in building construction, it is necessary to insulate and minimize air infiltration through walls. Typical wall construction to minimize air infiltration includes installing insulation between the studs and installing a vapor barrier, such as polyethylene, over the studs, and applying an interior wall covering such as sheetrock over the vapor barrier.
Unfortunately, the installation of conventional electrical boxes on the walls oftentimes compromises the air tightness of a building. Typically, electrical boxes are fastened to the studs and wiring pulled into the boxes prior to installation of the vapor barrier. The vapor and sheet rock are typically installed over the electrical boxes and holes then cut in the vapor barrier and sheetrock to expose the electrical boxes.
A couple of problems arise when holes are cut in the vapor barrier for conventional electrical boxes. Since the front edge of the electrical box extends to approximately level with the interior wall, the hole is typically cut larger than the periphery of the electrical box. With the hole larger than the electrical box, air seepage can occur around the periphery of the electrical box. The air seepage occurs as a result of the disruption of the integrity of the vapor barrier around the box and the inability of the conventional electrical box to create a proper seal with the vapor barrier.
A second source of air infiltration is through the conventional electrical box itself. This can occur as a result of oversized knockouts in the box and the lack of proper sealing materials around the electrical cables leading into the box.
Some manufacturers have attempted to solve the problem of air leakage through the box with multiple walls creating chambers into which foam can be inserted to surround incoming electrical cables. Although the foam can be sprayed into the chambers, it is difficult to control the amount of foam sprayed therein and the foam can frequently flow beyond the chambers and into the interior of the electrical box. Excess foam in the electrical box cavity can interfere with placement of an electrical device into the box. Additionally, with double-walled electrical boxes and the inherent problem of controlling the flow of the expanding foam, it is difficult to tell whether the foam has completely sealed around the cable entering the box or whether it has simply flowed into the internal cavity of the electrical box.
What is needed therefore is an electrical box that stops air infiltration around the periphery of the box and also enables proper sealing at the knockout areas wherein the electrical cables enter the box.